MOST stuff that gross you out does so because you were taught to be. For example, ask any westerner to eat an insect, they are going to say its gross. Hell, even as little as 20 years ago the idea of eating raw fish was gross as hell to the average westerner, but look at it now.

I once ate Taco Bell when I had the flu. I threw it all up and now Taco Bell grosses me out even though I didn't throw up because of Taco Bell but because of an independently contracted virus.

Point is, there are learned aversions and instinctual ones. Human beings have a fairly unique low level of instinctual aversion responses though these do fluctuate over a lifetime. Pregnant women for example, show aversions to different foods based on the probability of contracting harmful pathogens from them. The categories of foods that have different harm potentials each have different average aversion levels when measured for each trimester. You've heard of women having cravings and food aversions during pregnancy, right? It's an evolved response that can be predicted based on the danger of contracting a pathogen. Pretty cool huh?

Animals are grossed out by smells and tastes. They tend to not understand what they are seeing as appose to humans. So if you dropped a deuce within inches of a dog, the dog would repel from the smell. Not the sight itself. Another example, if a cat tasted poop it would be grossed out by the taste.